Formation of ring-shaped assembly of microtubules with a narrow size distribution at an air-buffer interface

Biopolymers such as actin, microtubules and DNA are well known for their fascinating in vivo self-organization phenomena. Considerable efforts have been devoted to mimicking their organization process in vitro that produced ring-shaped or toroid structures in an irreversible manner. However, understanding the factors that lead to formation of such assembled structures deserves more investigation to achieve a unified insight into the assembly process, particularly of the microtubules. Here, we report an active assembly process of microtubules (MTs) at an air-buffer interface that resulted in ring-shaped microtubule structures with a narrow size distribution and a high yield. Using an "air-buffer interface control system" combined with the newly developed "inert chamber system (ICS)" we have also successfully observed the reversible conformational transition between ring- and linear-shaped microtubules at the air-buffer interface. This is the first ever direct in situ observation of a reversible assembly process of MTs and probably provides us with valuable discernment to understand the in vivo organizational behavior of biopolymers.